Answer: $16.70
Step-by-step: Since she is mailing 3 large packages, and each costs $4.50 to mail, your equation would be 4.50 x 3. This equals to $13.50. Since you are mailing one more small package that costs $3.20 to mail, you would add $3.20 to $13.50, to get your answer of $16.70 :)